1. Field of the Invention
The present invention relates to a vulcanized rubber-metal plate composite which comprises a plurality of rubber layers and metal plates overlaid alternately, a method and an apparatus for heating an unvulcanized rubber-metal plate composite which is the original state of the vulcanized rubber-metal plate composite, and a method and apparatus for manufacturing the vulcanized rubber-metal plate composite.
2. Description of the Related Art
Vulcanized rubber-metal plate composites have been used in, for example, anti-seismic dampers or rubber bearings. The anti-seismic dampers are placed on the foundations of structures, e.g. buildings, bridges and machines to reduce response acceleration to excitation force due to earthquakes and thus to reduce damage to the structures. A typical anti-seismic damper for buildings has a large size, i.e., a design load over 500 tons and a diameter of approximately 1 meter.
Such a rubber-metal plate composite is manufactured by bonding a plurality of vulcanized rubber layers and metal plates alternately or by heating an unvulcanized rubber-metal plate composite to a vulcanization temperature while compressing it. A method for bonding the vulcanized rubber layers and the metal plates is disclosed in Japanese Patent Publication No. 59-19018, in which bonding layers are primarily heated by induction heating of the metal plates. Since this method requires a step for vulcanizing unvulcanized rubber layers one by one and a step for applying a bonding agent on the metal plates and overlaying the vulcanized sheets and the metal plates alternately, it is not desirable for large size composites such as anti-seismic dampers.
It is therefore preferred that a composite comprising unvulcanized rubber layers and metal plates is heated while being compressed to vulcanize the rubber layers. General methods for heating unvulcanized rubber include hot-plate pressing and hot pressing. Also, heating unvulcanized rubber due to heat transfer from a mold heated by electromagnetic induction is proposed in Japanese Patent Laid-Open No. 57-193340.
Since unvulcanized rubber is a heat-insulating material, the heating of rubber articles by means of an external heat source, e.g. a hot plate or a mold, needs a long time before the interior of the rubber is sufficiently heated, resulting in decreased productivity. Such a trend is noticeable in large size anti-seismic dampers. For example, a large anti-seismic damper for buildings having a design load of approximately 500 tons and a diameter of approximately 1 meter requires a vulcanization time of 10 to 20 hours. Heating while compressing such a large composite for a long time also consumes much energy resulting in increased production costs.